The Role of Organic Capping Layers of Platinum Nanoparticles in Catalytic Activity of CO Oxidation

It is shown that the conversion of ethanol-to-gasoline over an HZSM-5 catalyst yields essentially the same product distribution as for methanol-to-gasoline performed over the same catalyst. Interestingly, there is a significant difference between the identity of the hydrocarbon molecules trapped inside the HZSM-5 catalyst when ethanol is used as a feed instead of methanol. In particular, the hydrocarbon pool contains a significant amount of ethylsubstituted aromatics when ethanol is used as feedstock, but there remains only methyl-substituted aromatics in the product slate.     

Effect of Impurity and Pretreatment Conditions on the Catalytic Activity of Au Powder for CO Oxidation

Recent X-ray photoelectron spectrometer(XPS) analysis of Au powder synthesized by evaporating high purity gold metal (> 99. 99%) in an inert gas detected impurity metals such as Ag and In at levels which far exceed those expected from the impurity levels of raw gold metal. Several samples of Au powder containing different amount of impurity metals were prepared to examine whether the activity of the Au powder for CO oxidation depends upon the impurity or not. The activity of the powder showed a strong correlation with the surface concentration of Ag.     

Effect of Support Modification on Reduction and CO Oxidation Activity of Doped Ceria-Supported Copper Oxide Catalyst

Ceria materials were modified by doping with gadolinia or yttria and by a hold period at 260 °C for 2 h during temperature-programmed calcinations to 650 °C. These doped ceria-supported copper oxide catalysts and the doped ceria material were characterized by temperature-programmed reduction, electron paramagnetic resonance, and CO oxidation activity test. It was observed that, as the doping concentration of gadolinia increases, the reduction temperature of the copper oxide species increases and the CO oxidation activity decreases. This is due to increased formation of the surface spinel species of copper oxide with gadolinia. As the yttria content increases to greater than 10 mol%, surface segregation occurs, which causes the amount of surface oxygen vacancies to decrease. It was also found that maintaining the temperature at 260 °C during calcination may decrease the amount of oxygen vacancies. The surface oxygen vacancies may be the active sites for CO oxidation over the oxygen ion conducting materials in the absence of any metal present. Gd doping leads to the formation of extrinsic oxygen vacancies, which increases the oxygen ionic conductivity of the doped ceria and thus increases the CO oxidation activities of the supported catalysts as well as of the doped ceria.     

Cefditorene-Mediated Synthesis of Silver Nanoparticles and Its Catalytic Activity

Ag(0) NPs were prepared by chemical reduction method in which silver nitrate was taken as the metal precursor and cefditorene as a reducing/capping agent and NaOH as the catalyst for reaction enhancement. The formation of the Ag(0) NPs was monitored using UV–Vis absorption spectroscopy confirmed the formation of Ag(0) NPs by exciting the typical surface plasmon absorption maxima at 405 nm. Transmission electron microscopy (TEM) confirmed the spherical morphology of the (Ag(0) NPs). The crystallite (11 ± 3 nm) and particle size (14.1 ± 2.2 nm) obtained from TEM and XRD analysis were coinciding with each other. Prepared Ag(0) NPs were then used as catalyst against 2-nitroaniline, 3-nitroaniline and 4-nitroaniline, which all showed best catalytic activity.     

CO Adsorption on FeO x Nanoclusters Supported on HOPG—Effect of Oxide Formation on Catalytic Activity

CO adsorption on FeO _x clusters has been characterized by thermal desorption spectroscopy (TDS) and molecular beam scattering. Iron was vapor deposited and oxidized by annealing in O₂. The TDS curves consist initially of two peaks indicating formation of γ-Fe₂O₃/Fe₃O₄. Increasing the O₂ exposure results in one TDS peak and the dominance of α-Fe₂O₃.     

Catalytic Activity of Supported Platinum and Metal Oxide Catalysts for Toluene Oxidation

Oxidation of toluene has been investigated over supported platinum as well as over a variety metal oxide (M _x O _y ) catalysts dispersed on high surface area γ-Al₂O₃. Catalysts were characterized with respect to their specific surface area (BET), metal dispersion (selective chemisorption of CO), phase composition and M _x O _y crystallite size (XRD) and reducibility (H₂-TPR). Catalytic performance for the title reaction was investigated in the temperature range of 100–500 °C, using a feed composition consisting of 0.1% toluene in air. For Pt/M _x O _y catalysts, it has been found that catalytic performance depends on the nature of the support, with Pt/CeO₂ being the most active catalyst at low temperatures. The intrinsic reaction rate per surface platinum atom does not depend on Pt loading (0.5–5 wt%), at least for Pt/Al₂O₃. Reducible metal oxides, such as ceria, are active for the title reaction and catalytic performance is improved significantly with increase of specific surface area (SSA). However, the intrinsic reaction rate per unit surface area is invariant with SSA. Dispersion of M _x O _y on high surface area inert supports, such as Al₂O₃, results in materials with relatively high catalytic activity, which seems to correlate well with the reducibility of metal oxides. Catalytic performance of M _x O _y /Al₂O₃ catalysts can be optimized by proper selection of M _x O _y loading. Best performing catalysts of this series include 60% MnO, 90% CeO₂ and 5% CuO on Al₂O₃ which, under the present experimental conditions, are able to completely convert toluene toward CO₂ at temperatures lower than 350 °C. Dispersion of Pt on M _x O _y /Al₂O₃ catalysts improves significantly the catalytic performance of irreducible M _x O _y but does not alter appreciably the activity of reducible M _x O _y /Al₂O₃ catalysts.     

Catalytic Oxidation of CO Over Synthesized Nickel Ferrite Nanoparticles from Fly Ash

Catalytic oxidation of carbon monoxide (CO) gas over nanosized nickel ferrites prepared from fly ash has been investigated. X-ray diffraction analyses showed that pure crystalline nickel ferrite, NiFe₂O₄, phase can be obtained by thermal treatment of the precursors at temperature >800 °C for 120 min in the studied pH range, from 7 (neutral) to 12 (highly alkaline). In the temperature range 500 ≤ T ≤ 800 °C, impure low crystalline NiFe₂O₄ phase formed. The main impurities are FeO (OH) and Fe₂O₃ · H₂O phases. Higher magnetization (32 emu/g) is obtained for a precursor precipitated at pH 10 and thermally treated at 1,200 °C for 120 min. The catalytic oxidation of CO over nanocrystalline NiFe₂O₄ powders was studied using quadrupole mass gas analyzer system. The main parameters as crystal size, surface area and firing temperature are used to clarify the efficiency of using NiFe₂O₄ powders in catalytic oxidation of CO. It was found that the efficiency of catalytic oxidation decreased by increasing firing temperature and crystallite size of the samples. The lower crystal size (2–8.5 nm), the higher surface area (25–55 m²/g) and the presence of impurities FeO(OH) phase enhanced CO adsorption and consequently its oxidation.     

High Catalytic Activity in CO Oxidation over MnO x Nanocrystals

Manganese oxides of various stoichiometry were prepared via Mn-oxalate precipitation followed by thermal decomposition in the presence of oxygen. A non-stoichiometric manganese oxide, MnO _x (x = 1.61…1.67) was obtained by annealing at 633 K and demonstrated superior CO oxidation activity, i.e. full CO conversion at room temperature and below. The activity gradually decreased with time-on-stream of the reactants but could be easily recovered by heating at 633 K in the presence of oxygen. CO oxidation over MnO _x in the absence of oxygen proved to be possible with reduced rates and demonstrated a Mars—van Krevelen—type mechanism to be in operation. A TEM structural analysis showed the MnO _x phase to form microrods with large aspect ratio which broke up into nanocrystalline manganese oxide (MnO _x ) particles with diameters below 3 nm and a BET specific surface area of 525 m²/g. Annealing at 798 K rather than 633 K produced well crystalline Mn₂O₃ which showed lower CO oxidation activity, i.e. 100% CO conversion at 335 K. The catalytic performance in CO oxidation of various Mn-oxides either studied in this work or elsewhere was compared on the basis of specific reaction rates.     

金属氧化物纳米粒子对沥青质氧化的催化作用

使用热重分析研究了不同金属氧化物纳米粒子在等温条件下对沥青质热氧化分解的催化作用。为了找到一种采出沥青质的新方法,研究了3种不同的金属氧化物纳米粒子对沥青质热氧化的催化作用,它们分别为:NiO、Co_3O_4和Fe_3O_4。结果表明,纳米粒子的存在可以降低沥青质氧化过程中的活化能并提高反应速度。可以看出,热力学氧化反应是金属氧化物特有的反应。得到的动力学数据表明,在NiO的催化下,沥青质质的反应速度最高,其次是Co_3O_4,最后是Fe_3O_4,各种金属氧化物纳米粒子的催化性能不同反映出了反应机制的不同。     

纳米氧化铁的制备及其掺杂效应

纳米氧化铁作为气敏材料得到广泛重视。本文重点介绍了近年来应用比较普遍的合成纳米氧化铁的方法,如:溶胶—凝胶法、共沉淀法、水热法、水解法,并指出了各种方法的优缺点;同时,介绍了在掺杂了不同的物质后纳米氧化铁具有的独特的气敏性能;最后,对氧化铁基气敏元件的烧成工艺进行了比较。     

ZrO_2负载Cu催化剂对CO低温催化氧化研究

用溶胶-凝胶-超临界干燥法制备了纳米氧化锆。采用沉淀法制备氧化锆负载铜催化剂。制备的催化剂用X-ray射线衍射(XRD),透射电镜(TEM),比表面积(BET)和H2-TPR等进行了表征。研究了催化剂的焙烧温度和负载比例对CO转化效率的影响,其最佳焙烧温度为650℃,Zr与Cu的最佳物质的量比是10:8。获得催化剂在温度为68℃具有催化活性,176℃时CO的转化率达到50%,较好地实现了ZrO2负载Cu在较低温度下对CO的催化。     

纳米银粒子的制备及其催化性能的研究

采用化学还原的方法,以聚乙烯吡咯烷酮为稳定剂,硼氢化钠为还原剂合成了纳米级银粒子。TEM和XRD分析表明所制备的银纳米粒子粒径分布窄,其平均粒径为15nm左右,且具有较高的结晶度。进一步催化硼氢化钠还原甲苯胺蓝的实验表明该银溶胶具有较高的催化活性。     

Effect of Additives on the Physicochemical and Catalytic Properties of Oxide Catalysts in Selective Oxidation Reactions

This paper is a survey of the main facts and concepts concerning the effect of additives on the structure and physicochemical and catalytic properties of oxide catalysts in selective oxidation reactions. The phenomena occurring in monophasic and supported mixed oxides containing the additives, including modification of structure, solid state reactions, segregation, defect formation, and spill-over of the reactants, are briefly described. The effect of additives on acid--base and redox properties, and on their bearing on catalytic performance are discussed, with particular emphasis on alkali metal additives. The perspectives of further studies on the problem are proposed.     

碘纳米粒子掺杂TiO_2的表征及其可见光催化活性研究

以钛酸四正丁酯为钛源,用溶胶-凝胶法制备氨基化纳米TiO_2,并掺杂碘纳米粒子制备I-TiO_2,研究其光催化性能。结果表明,掺杂碘纳米TiO_2对光催化反应更好,经煅烧的I-TiO_2的光催化降解率更高,碘掺杂量为Ti∶I=1∶0.1(摩尔比)的催化剂效果最好。     

Eu3+ and Lysine Co-intercalated α-Zirconium Phosphate and Its Catalytic Activity for Copolymerization of Propylene Oxide and CO2

A novel composite material, α-Zr(HPO₄)₂·1.5Lysine:0.06Eu³⁺ (designated ZLE), has been prepared through intercalation of L-lysine (Lys) molecules and Eu³⁺ ions into between the layers of α-Zr(HPO₄)₂ (α-ZrP). It is proposed that the ZLE material contains Eu complexes lying between adjacent layers of Lys molecules which are attached on the inner surface of α-ZrP, and the Eu³⁺ ions are coordinated by carboxyl groups of Lys molecules. The ZLE composite in combination with Al(i-Bu)₃ and glycerin has been used as a catalyst for the copolymerization of propylene oxide (PO) and CO₂, and the catalytic system exhibits performance superior to the previously reported Y(P₂₀₄)₃-Al(i-Bu)₃-glycerin system.     

ZrO2负载铜镍双金属对CO低温催化活化研究

用两种方法合成载体ZrO2,分别负载镍单金属和铜镍双金属制备催化剂,对其做CO催化,确定载体最佳制备方法。用最佳方法制备的载体负载铜镍金属做催化剂,考察催化剂焙烧温度和负载比例不同对CO催化影响。实验结果表明,用溶胶凝胶超临界干燥法制备的ZrO2为载体负载铜镍制备的催化剂其最佳焙烧温度为250℃,Zr与Cu和Ni的最佳物质的量比是10：8：4时,获得催化剂起始催化活性温度为22℃,169℃时C0的转化率达到50％,较好地实现了ZrO2负载铜镍在较低温度下对CO的催化。